The present invention relates to testing materials and more particularly to a self-examination system wherein multiple copies are prepared by spirit duplication of a preprinted master containing latent images which on the copy sheet are developed on contact with a chemical reactant.
With the ever increasing work load on teachers and instructors, it becomes important to use modern technology to relieve the teacher of some of the duties ordinarily undertaken. Thus, it is possible to have pre-printed spirit duplicating masters of examination forms from which the teacher can make copies for testing the students on a given subject.
Self-instructional materials also find ever increasing utility in today's education system. This convenience may include a self-examination system wherein the test sheet contains both visible and invisible images. The questions are printed in visible ink while the correct answers for each question are printed in areas in invisible ink. After marking his selection, the student uses a solvent or chemical revealing the correct answers for his selection. This type self-examination system is discussed in U.S. Pat. Nos. 3,363,336; 3,363,337 and 3,363,338.
In U.S. Pat. No. 3,451,143 there is disclosed a similar system in which the test copy containing the latent images are prepared by spirit duplication. The invisible image on the spirit duplicating master may be, for example, nickel acetate in a carnauba wax - oil formulation. The spirit fluid effects transfer of the invisible image of the master to the copy sheet. A developing fluid such as dithiooxamide in methanol is used to form the color reaction. It is also disclosed that visible images may be placed on the same copy sheets from separate or the same master. In either event, one or two transfer sheets are necessary to prepare the masters, presenting a problem for the teacher when making the master for preparing the test copies.
Such a system has also been criticized because the reactant must remain chemically dormant on the surface of the sheet for hours, days, or even months. Thus, in U.S. Pat. No. 3,682,673 to Manske, it is pointed out that when dithiooxamide is the latent image on the sheet, since it has at least some vapor pressure at room temperature, these sheets have a poor shelf-life. Accordingly, Manske suggests a system wherein the dithiooxamide reactant is encapsulated and coated on the surface of a sheet which is juxtaposed with a receptor sheet. When the microcapsules are crushed in the selected area, the latent image is transferred to the receptor sheet, which is then developed at a later time by applying to the receptor sheet a metal salt along with the solvent for the dithiooxamide reactant. This color reaction and encapsulation process is also shown in U.S. Pat. No. 3,287,154.
While encapsulation may be one solution to the problems of shelf-life present in the spirit duplicating system of U.S. Pat. No. 3,451,143, it has additional problems in that either high speed printing must be used to prepare numerous test copies well in advance of the exam or each test must be individually typewritten. Manske prepares test copies but not a spirit duplicating master for making the copies.
Therefore, the need exists for a spirit duplicating system which uses reusable pre-printed masters having a good shelf-life so that the teacher can easily prepare the exact number of test copies needed from the master for immediate self-instructional use by the students.